The present invention relates to an apparatus for monitoring a video signal level and, more particularly, to an apparatus for monitoring a level of an NTSC (National Television System Committee) composite signal converted from a Y/color difference component signal.
Video signals such as a Y/color difference component signal and an NTSC composite signal are specified in accordance with various systems. Ordinarily, in broadcasting stations, a Y/color difference component signal is converted into an NTSC composite signal, and the NTSC composite signal is transmitted.
However, the range of the maximum amplitude level of the Y/color difference component signal is wider than the level range in which the NTSC composite signal is controlled. For this reason, the level of the NTSC. composite signal is not suitably controlled when level control only on the Y/color difference component signal is performed. Therefore there has been a demand for a level control method devised by considering an effect after conversion into the NTSC composite signal.
In general, the NTSC composite signal is encoded in accordance with the SMPTE170M standard established by the Society of Motion Picture and Television Engineers (SMPTE). Therefore, there is a need to control the level of the NTSC composite signal in the range (−40 IRE to +131 IRE) in accordance with the SMPTE170M standard shown in FIG. 1. There is a need to control the level of the luminance component (Y) in particular in the NTSC composite signal so that it does not exceed 120 IRE.
FIG. 2 is a diagram showing a display for controlling the level of the NTSC composite signal converted from the Y/color difference component signal as described in a non-patent document 1 shown below. The conventional method using the display shown in FIG. 2 enables control as to whether the level of the NTSC composite signal (a vector formed of a luminance component and a color component) is within the range in accordance with the SMPTE170M standard mapped on the Y-color difference plane.
[Non-Patent Document 1]
Tektronix Japan, Ltd., “GAMUT Measurement” (FIG. 5), [online], [search on Dec. 13, 2003], Internet<URL: http://www.Tektronix.co.jp/Products/Measurement_Prod/App_no tes/wfm700_gamut_measure.pdf>.